What exactly is supposed to happen when a direct gas impingement system is fired with a suppressor w/o modifications on the gas valve? Will the overpressure cause the system to kinda explode or will it just malfunction?

I have done it many thousands of times and as far as I know, absolutely nothing happened other than the bullet going down range and the action cycling. And.........it wasn't as loud.

In fact, this is the first time I have ever heard that something MIGHT happen.

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You know the rest. In the books you have read
How the British Regulars fired and fled,
How the farmers gave them ball for ball,
From behind each fence and farmyard wall,
Chasing the redcoats down the lane,
Then crossing the fields to emerge again
Under the trees at the turn of the road,
And only pausing to fire and load.

That's good to hear. I'm awaiting for my suppressor to come in and I'm trying to look into what "mods" I need to do to my AR (pistol length gas system). Adjustable gas block, heavier buffer, stronger buffer spring, etc. I'll just leave the gun alone and see what happens when the suppressor comes in.

"gas valve" is the wrong term, but I reckon there is a gas block that in some assault rifle types can be adjusted to firing rifle grenades, using blanks and - or so it appears to me - also for the use of a suppressor. Might be that this is only the case for other systems like long / short stroke and not for the direct impingement?

Yes you can have an adjustable gas block. Most rifles don't come that way but you can put one on if there is some reason you need it. And you can use it to tune your rifle.

But if your rifle is running fine the way it is, there isn't much point in getting one.

I have never had an adjustable gas block. FWIW: I probably own a dozen AR15 uppers and have owned an AR15 since about 1982.

__________________
You know the rest. In the books you have read
How the British Regulars fired and fled,
How the farmers gave them ball for ball,
From behind each fence and farmyard wall,
Chasing the redcoats down the lane,
Then crossing the fields to emerge again
Under the trees at the turn of the road,
And only pausing to fire and load.

Well, sort of. All of my hosts have adjustable gas blocks or adjustable piston systems.
I wouldn't say "there's no concern" when adding a suppressor to a DI gun but it's not likely to explode. There is a concern that increasing the back pressure can cause undue wear and tear on the components so many users swap in a heavier buffer or adjustable gas block(and some don't). If the residual barrel pressure is excessive, the bolt may not close properly and may even cycle a "double feed".

Right Mobuck, if you add a suppressor to an AR15, you will increase the pressure in the gas system. Depending on how the gun is set up, whether is is a carbine, mid length, or rifle length system, spring weight, buffer weight, etc., the addition of the suppressor most definitely CAN introduce cycling problems due to over pressure. Your BCG will likely cycle much faster as a result (which brings up the additional wear and tear you mentioned). Adjustable gas blocks can help mitigate the issue considerably.

You may find that if you have brass ejecting at 3-4 o'clock before adding the suppressor, that it starts landing at 1-2 o'clock. On a calm day or indoor range, you will likely notice a puff of hot gasses into your face, coming out around the charging handle after you add a suppressor.

The faster bolt speed will cause the carrier & bolt parts to wear out faster - although this typically isn't noticeable for most users.

Since the bolt is cycling faster, it's possible to actually outrun the spring in your magazine. (This is often referred to as Bolt-Over-Base.) In this case, your weapon will either jam or lock up on an empty chamber.

The weapon will get dirtier faster since there is more gas in the chamber.

You'll generally smell more gas; and, depending on the weapon, may feel it blowing into your face & eyes as you shoot.

I know that with 6.5 Grendel and 6.8 SPC AR15s, the addition of a suppressor will foul the cartridges in your magazine as you fire with each shot. Cartridges will be sooted, may tarnish, and you may actually get a build-up of gunk on them. This is from personal experience. It happens to a much lesser extent with .223/5.56.

Also, you do not want to leave cartridges chambered in your AR15 overnight or for long periods of time after firing several rounds. The cases can tend to stick in the chamber and may or may not cycle properly as a result. Extracting them manually can be extremely difficult. If you are storing a loaded, suppressed AR15 for SD purposes, store one that is clean.

While it may be correct to say that it is just a muffler, mufflers on engines affect how engines run via back pressure. So back pressure is an issue not just with the AR15, but with engines as well. https://en.wikipedia.org/wiki/Back_pressure

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A suppressor is nothing more than a muffler. Just like the one in your car. It doesn't fiddle with the gases at all. It fiddles with the sound created by them.

This is the second time I've seen you post this, and it's the second time I've pointed out that it's wrong. Every rifle silencer on the market except those from OSS will increase the gas pressure. Usually the rifle will still run just fine without modification, but not always.

What exactly is supposed to happen when a direct gas impingement system is fired with a suppressor...

In general, nothing out of the ordinary.

Suppressors/silencers work by redirecting the propellant gasses leaving the muzzle through a series of chambers where it can expand slowly enough that it is no longer supersonic when it enters the atmosphere.

__________________
"If you look through your scope and see your shoe, aim higher." -- said to me by my 11 year old daughter before going out for hogs 8/13/2011
My Hunting Videos https://www.youtube.com/user/HornHillRange

In my experience the only cartridge that doesn't "foul the ammo in the magazine" is the 300BO. Even my AA piston uppers do this but to a lesser extent. I expected the piston system to take care of this but evidently the back pressure in the barrel is sufficient to blow carbon back past the case as the bolt is opening. A heavier buffer might decrease this but it's only what I'd call cosmetic so I haven't tested this idea.

Perhaps I should have been more pedantic and said that nearly all standard AR15's come with a fixed gas block, i.e. either a standard triangle front sight or a low profile gas block and only modified, rifles either factory or owner modified, will have adjustable gas port regulation.

While I know that there is likely to be some difference in port pressure between suppressed and non suppressed gas operated firearms, in the two examples I am familiar with, I can't feel any noticeable difference in felt recoil.

One is a standard 14.5" barreled M4gery with a AAC M4-2000 and the other is a SBR with a 10.5" barrel, running the same M4-2000. Both have standard carbine length gas systems and both cycle perfectly w/o the can. I expected the recoil to increase enough to notice when the suppressor in on the M4gery and was surprised that it felt the same.

On the SBR, I was concerned that I would have some cycling issues due to the extremely short dwell time after the gas port, but it seems to work okay unsuppressed and, like the other rifle, I can't notice any difference in felt recoil with the can on it. I have seen no evidence of increased wear on the bolt components but then I only have a few thousand rounds through it.

I do replace the gas rings from time to time, but I consider that to be a part of the normal maintenance on a gas operated AR.

A friend of mine has a 10.5" SBR that he runs with a AAC M42K. When he first got the suppressor, the increased back pressure caused the gun to jam (bolt over ride) on just about every shot. A H3 buffer cured that problem. After that the only issue was the gas that blew out around the charging handle. A gasbuster handle with some gasket goo cured that problem.

In the case of my SCAR, I switch the gas block to the suppressed setting and have no problems other than the increased fowling in the receiver. I have not seen a suppressor that will not blow additional carbon into the chamber / receiver during extraction.

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"9mm has a very long history of being a pointy little bullet moving quickly" --Sevens

The AR15 bleeds off excess gas through the two holes in the bolt carrier group as the gas pushes the bolt/gas rings back in the carrier. So it can already adjust itself some for excess gas pressure. However, where the gas port has been opened up to compensate for a short dwell time (10" barrels, 16" with rifle gas), adding a suppressor can cause a problem. LMT even makes a three-hole bolt carrier to address that.

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